Transmission device and distortion compensation method

Abstract

A storage unit stores a first lookup table including a plurality of correction coefficients for I codes, and stores a second lookup table including a plurality of correction coefficients for Q codes. Each of the correction coefficients for I codes and each of the correction coefficients for Q codes are complex numbers. A distortion compensation unit compensates, with one of the plurality of correction coefficients for I codes, distortion of an I code of a transmission signal to generate a first input signal, outputs the first input signal to an SCPA for I codes. The distortion compensation unit compensates, with one of the plurality of correction coefficients for Q codes, distortion of a Q code of the transmission signal to generate a second input signal, and outputs the second input signal to an SCPA for Q codes.

What is claimed is: 
     
       1. A transmission device comprising:
 a storage unit that independently stores a first lookup table that includes a plurality of correction coefficients for I codes, and a second lookup table that includes a plurality of correction coefficients for Q codes, each of the plurality of correction coefficients for I codes and each of the plurality of correction coefficients for Q codes being complex numbers; 
 a distortion compensation unit that compensates, with one of the plurality of correction coefficients for I codes, distortion of an I code of a transmission signal to generate a first input signal, and compensates, with one of the plurality of correction coefficients for Q codes, distortion of a Q code of the transmission signal to generate a second input signal; 
 a first switched-capacitor power amplifier that amplifies the first input signal; and 
 a second switched-capacitor power amplifier that amplifies the second input signal, 
 wherein the number of correction coefficients for I codes included in the first lookup table is a number of non-overlapping adjustment values for I codes, each of the non-overlapping adjustment values for I codes being a value for adjusting a non-overlapping period where both a first switch and a second switch included in the first switched-capacitor power amplifier are in an off-state, with the first switch located between a first power supply and a first output terminal of the first switched-capacitor power amplifier, and the second switch located between the first output terminal and a ground; and 
 the number of correction coefficients for Q codes included in the second lookup table is a number of non-overlapping adjustment values for Q codes, each of the non-overlapping adjustment values for Q codes being a value for adjusting a non-overlapping period where both a third switch and a fourth switch included in the second switched-capacitor power amplifier are in an off-state, with the third switch located between a second power supply and a second output terminal of the second switched-capacitor power amplifier, and the fourth switch located between the second output terminal and the ground. 
 
     
     
       2. The transmission device according to  claim 1  further comprising a switch that switches between input of the transmission signal and input of a test signal for training of correction coefficients, wherein
 the switch input the test signal to the distortion compensation unit, 
 the distortion compensation unit uses the test signal to generate the correction coefficients for I codes and the correction coefficients for Q codes, and 
 the storage unit stores the correction coefficients for I codes that are generated using the test signal in the lookup table for I codes and stores the correction coefficients for Q codes that are generated using the test signal in the lookup table for Q codes. 
 
     
     
       3. The transmission device according to  claim 1 , wherein the storage unit stores a common lookup table that operates as both of the first lookup table and the second lookup table. 
     
     
       4. The transmission device according to  claim 1 , wherein the distortion compensation unit comprises:
 a first multiplier that multiplies the I code of the transmission signal by one of the plurality of correction coefficients for I codes; 
 a second multiplier that multiplies the Q code of the transmission signal by one of the plurality of correction coefficients for Q codes; and 
 a first adder that adds a real part of a multiplication result of the first multiplier, and an imaginary part of a multiplication result by the second multiplier, to obtain the first input signal; and 
 a second adder that adds an imaginary part of the multiplication result by the first multiplier, and a real part of the multiplication result by the second multiplier, to obtain the second input signal. 
 
     
     
       5. The transmission device according to  claim 1 ,
 wherein the plurality of correction coefficients for I codes included in the first lookup table are associated with respective ones of a plurality of non-overlapping adjustment values, and 
 the plurality of correction coefficients for Q codes included in the second lookup table are associated with respective ones of the plurality of non-overlapping adjustment values. 
 
     
     
       6. The transmission device according to  claim 4 , further comprising:
 an interpolation value processing unit that performs linear interpolation of correction coefficients using the plurality of correction coefficients for I codes and the plurality of correction coefficients for Q codes to obtain an interpolation value. 
 
     
     
       7. The transmission device according to  claim 1 , wherein:
 the first switched-capacitor power amplifier inputs the first input signal as an AM code, and uses the I code of the transmission signal as a non-overlapping switching signal, and 
 the second switched-capacitor power amplifier inputs the second input signal as an AM code, and uses the Q code of the transmission signal as a non-overlapping switching signal. 
 
     
     
       8. The transmission device according to  claim 1 , further comprising:
 a phase rotation unit that rotates a phase of the I code and a phase of the Q code of the transmission signal; and 
 an update processing unit that uses the I code and the Q code whose phases are rotated, to update the plurality of correction coefficients for I codes and the plurality of correction coefficients for Q codes stored in the storage unit. 
 
     
     
       9. A distortion compensation method comprising:
 updating a first lookup table that includes a plurality of correction coefficients for I codes, and a second lookup table that includes a plurality of correction coefficients for Q codes, each of the plurality of correction coefficients for I codes and each of the plurality of correction coefficients for Q codes being complex numbers, the first lookup table and the second lookup table being independently stored; 
 compensating, with one of the plurality of correction coefficients for I codes, distortion of an I code of a transmission signal to generate a first input signal, and inputting the first input signal into a first switched-capacitor power amplifier; and 
 compensating, with one of the plurality of correction coefficients for Q codes, distortion of a Q code of the transmission signal to generate a second input signal, and inputting the second input signal into a second switched-capacitor power amplifier, 
 wherein the number of correction coefficients for I codes included in the first lookup table is a number of non-overlapping adjustment values for I codes, each of the non-overlapping adjustment values for I codes being a value for adjusting a non-overlapping period where both a first switch and a second switch included in the first switched-capacitor power amplifier are in an off-state, with the first switch located between a first power supply and a first output terminal of the first switched-capacitor power amplifier, and the second switch located between the first output terminal and a ground; and 
 the number of correction coefficients for Q codes included in the second lookup table is a number of non-overlapping adjustment values for Q codes, each of the non-overlapping adjustment values for Q codes being a value for adjusting a non-overlapping period where both a third switch and a fourth switch included in the second switched-capacitor power amplifier are in an off-state, with the third switch located between a second power supply and a second output terminal of the second switched-capacitor power amplifier, and the fourth switch located between the second output terminal and the ground. 
 
     
     
       10. The transmission device according to  claim 1 , wherein the first lookup table includes a first vector of N number of correction coefficients for I codes and the second lookup table includes a second vector of N number of correction coefficients for Q codes, N being an integer larger than one and the first vector and second vector being independent of each other. 
     
     
       11. The transmission device according to  claim 1 , wherein:
 when a non-overlapping adjustment value for I code is switched, a different correction coefficient for I codes is used, and 
 when a non-overlapping adjustment value for Q code is switched, a different correction coefficient for Q codes is used. 
 
     
     
       12. The distortion compensation method according to  claim 9 , wherein the first lookup table includes a first vector of N number of correction coefficients for I codes and the second lookup table includes a second vector of N number of correction coefficients for Q codes, N being an integer larger than one and the first vector and second vector being independent of each other. 
     
     
       13. The distortion compensation method according to  claim 9 , wherein:
 when a non-overlapping adjustment value for I code is switched, a different correction coefficient for I codes is used, and 
 when a non-overlapping adjustment value for Q code is switched, a different correction coefficient for Q codes is used.